Difficult as it might be to imagine today, at one time Canadians did not even require passports to visit the United States. Then came the terrible events of Sept. 11, 2001, and it was soon clear that those days of going through little more than a casual inspection to cross the international border were coming to an end.

In 2004, the National Commission on Terrorist Attacks Upon the United States — better known as the 9/11 Commission — released its report on the Sept. 11 attacks, and recommended that Canadians, Mexicans and Bermudans be required to show passports or other secure documents proving their identity to enter the United States. The same rule would apply to Americans returning from those countries.

Prior to this, many Canadians had never owned a passport. It wasn’t necessary to have one if you were travelling to the United States — which offered a range of destinations from big cities to mountains to coastal resorts — so few bothered to apply for one.

In any case, obtaining a Canadian passport came with its own archaic rules which seemed to assume that most Canadians still lived in small towns, as we had a century earlier. For example, you were required to have a guarantor from among a limited list of professions deemed trustworthy by the federal government. If you didn’t personally know a professional engineer, local mayor, ordained minister or postmaster for at least two years, you could always ask your dentist or doctor for the favour.

But the Canadian government quickly realized a big change was coming, and began to simplify the process of applying for a passport.

The official announcement came on Nov. 22, 2006, in a U.S. State Department news release: “The requirement for citizens of the United States, Canada, Mexico, and Bermuda to present a passport to enter the United States when arriving by air from any part of the Western Hemisphere will begin on January 23, 2007.” It was expected that the passport requirement for land or sea crossings would take effect by Jan. 1, 2008.

In just a few years, Canadian passport ownership rates rose significantly. In 1999-2000, the Canadian government had issued a little over 1.5 million passports to a population of 30 million. In 2005-06, it issued more than 3.1 million passports.

Ten years after the U.S. passport requirement went into effect, Statistics Canada data shows that those new passports gave Canadians a case of wanderlust that still hasn’t subsided.

The red squares on the graph below show the number of Canadians returning from countries other than the United States annually between 1972 and 2015.

The green circles represent the growth trend line based on the period from 1987 (when airline deregulation allowed lower international fares to be offered) to 2001 (when the 9/11 attacks shattered the status quo).

The green circles suggest that the 1987 deregulation did not give Canadians a newfound urge to go out and explore the outside world. Even if you had no idea how many Canadians came home from abroad each year in the ’70s and ’80s, merely extending the 1987-2001 trend line back to 1972 would have given you a decent estimate. After 1987, the number of Canadians coming home from abroad each year continued growing until 2003 on a trajectory not much different from the 1972-1987 trajectory.

In 2004, something changed. That year, the number of Canadians coming home from countries other than the U.S. was 13 percent higher than the year before — the first time since 1987 that year-over-year growth had exceeded 10 percent. In fact, during the preceding 10 years, five percent year-over-year growth had been more typical.

Thereafter, growth charged ahead at eight to nine percent per year until 2008, and then slowed to more anemic levels usually under five percent between 2009 and 2013. In 2014 and 2015, growth surged again at about 10 percent in both years.

By this time, the 1987-2001 trend line had clearly been departed from, and a new trend line had taken its place. Had nothing changed, the number of Canadians coming home from abroad should have risen from a little over five million in 2004 to about seven million in 2015.

Instead, it took only three years to hit seven million, and another year to hit eight million — a figure it otherwise should not have reached until about 2018 had nothing changed.

In reality, in 2015 alone, more than 11.5 million Canadians had come home from countries other than the U.S. Year-over-year growth in the first 10 months of 2016 was relatively weak — about three to four percent overall — so the final number for 2016 should be around 12 million once that information is available.

The 2007 U.S. passport requirement was a rule change that many Canadians weren’t fond of at first. But its introduction unleashed a desire among Canadians to go out and see the world beyond North America, hopefully coming home not just rested and relaxed, but with a bit of fresh thinking as well.

That’s cause enough to wish America’s passport requirement a happy 10th birthday indeed. Now if only we could do something about that stingy two weeks’ annual holiday thing we’ve got in our labour laws.